This invention relates to methods and apparatus for regulating battery discharge, and more particularly, to a method and apparatus for controlling power drawn from a battery in a battery powered computing system.
Conventional batteries for portable computers include lithium ion (Li-(Li-ion) battery packs, nickel metal hydride (NiMH) and nickel cadmium (xe2x80x98NiCadxe2x80x99) battery packs. The power sourcing capability of a battery pack is typically the product of the number of battery cells in the pack and the maximum power that can be produced by a single cell. The discharge current drawn from a battery pack is based upon the load requirements. For portable computers the load requirement is continually increasing as more powerful, and feature-rich systems are desired. Thus, advances in processor technology, for example, result in processors with correspondingly increasing power needs.
Problems arise, however, in sourcing increased discharge current to meet the increased power needs of advancing technology. As the discharge current rises, the temperature of the battery source increases. When the discharge current becomes excessive, the temperature of the cells may increase toward a critically high level, beyond which the battery cells become irreparably damaged. To prevent such excessive temperature condition, the battery halts its discharge when the discharge current exceeds a safety limit. As a result, the load loses power. For a computer, such loss of power can result, undesirably, in a loss of data. Accordingly, there is a need to avoid loss of power and corresponding loss of data in a computer system when the load begins to demand power from the battery system which is beyond acceptable limits.
According to the invention, a processor""s power requirement is reduced when the battery pack approaches its critical temperature. This reduces the battery discharge current, in turn causing the battery pack to generate less heat. The battery pack temperature thus remains safely below the critical temperature.
Battery discharge current is measured. According to one aspect of the invention, when a discharge current measuring circuit detects that the discharge current exceeds a first threshold current level, a throttle signal is sent to the system""s CPU chip set. In response, the chip set modulates a CPU stop control line to reduce power consumption. In brief, the CPU halts while the stop control line is active. As the stop control line modulates, the CPU is slowed according to the duty cycle of the stop modulation.
A delay occurs between assertion of the throttle signal and the commencement of the CPU stop modulation operations. When the discharge current falls below the threshold current value (or a second threshold current value), the throttle signal is withdrawn. In various embodiments the second threshold is less than the first threshold to provide a hysteresis effect. In addition or alternatively, a time delay is imposed before the throttle signal is withdrawn.
While the throttle signal is active, the CPU stop control line is modulated at a specific duty cycle. During the active part of the duty cycle, the CPU is stopped. During the inactive portion, the CPU operates normally. Accordingly, the CPU is stopped periodically to reduce the power consumption of the CPU, and correspondingly, to reduce the discharge current being drawn from the battery pack.
According to another aspect of the invention, in some embodiments the duty cycle for the CPU stop control line is controlled as a function of the excess discharge current (i.e., actual discharge current level less threshold current level). The more excessive the actual discharge current, the larger the duty cycle on the CPU stop modulation line. Thus, the more excessive the discharge current, the more time, proportionately, that the CPU is stopped and the greater the degree that CPU power consumption is reduced.
An advantage of the invention is that a smaller battery pack can be used safely with an increasingly powerful CPU. In particular, when the computing system is operating on line current in AC mode without the battery, the CPU can operate at full speed drawing the power as needed to maximize system performance. When the system is operating off the battery pack, performance will not be affected for many applications where excessive power is not drawn. Performance is traded off under high power draining conditions in exchange for the reduced cost and lighter weight of a smaller battery pack. As a result, a smaller battery pack is used safely to meet the needs of many computing applications. This may be particularly beneficial for the value segment of the portable computing market where cost is a significant factor. These and other aspects and advantages of the invention will be better understood by reference to the following detailed description taken in conjunction with the accompanying drawings.